Semiconductor Diode Experiment

Exploring Semiconductor Junction Diodes: An In-Depth Experiment

Introduction:

Semiconductor junction diodes play a crucial role in electronic circuits, allowing current flow in only one direction. This experiment aims to delve into the characteristics of diodes, focusing on V-I (voltage-current) curves and exploring the properties of zener diodes. By utilizing various equipment and components, participants will gain hands-on experience and insights into the behavior of semiconductor devices.
Components and Equipment:

1. Digital Multimeter (DMM)
2. DC Power Supply
3. Signal Generator
4. Oscilloscope
5. 1N4148 Diode
6. Zener Diode
7. 1K Resistor

Theoretical Background:

Diodes are semiconductor devices with the ability to allow current flow in one direction. Composed of a p-n junction, they are made from materials with positive (p-type) and negative (n-type) doping. Silicon diodes typically have a barrier potential of 0.7 V, and they conduct current when the anode voltage is 0.7 V higher than the cathode.The Diode Equation, representing the V-I characteristics, involves parameters like the saturation current (IS), thermal voltage (VT), and an arbitrary parameter 'n'. Diodes operate in three regions: reverse breakdown, reverse biased, and forward biased. Small signal ac models reveal dynamic resistance, and for forward-biased diodes, dynamic resistance (rd) can be calculated using the equation kT/q.
Zener diodes, designed to leverage the Zener breakdown region, exhibit a constant breakdown voltage, making them essential in regulated power supplies.
Experiment Procedure:

1. Diode Test:
   1. Use the diode-testing scale on the DMM to determine diode conditions.
   2. Perform tests for the Si diode, checking forward and reverse bias.
2. Diode Characteristics:
   1. Build a basic diode circuit and measure diode voltage as the power supply varies.
   2. Calculate diode current and plot the V-I characteristic.
   3. Draw a tangent line and determine incremental resistance.
3. Zener Diode:
   1. Replace the diode with a Zener diode in the circuit.
   2. Measure diode voltage, calculate diode current, and plot the V-I characteristic.
   3. Apply negative voltages and record results.

Experiment Procedure:
Note: Before starting the experiment, ensure you have received proper instructions from the instructor.
1. Diode Test
1.1. Diode Testing Scale:

• Set the DMM to the diode testing scale.
• Connect the diode as per Figure 5 for Si diode testing.
• Record readings for both forward and reverse biases in Table-1.
• Analyze the results to determine the diode's condition.

1.2. Resistance Scale:

• Use the resistance scale on the DMM.
• Connect the diode to measure resistance levels in forward and reverse biases.
• Record readings in Table-2.

2. Diode Characteristics:
2.1. Basic Diode Circuit:

• Construct the circuit shown in Figure 6.
• Gradually vary the power supply voltage from 0 to 10 volts.
• Record Diode Voltage (VD) and Resistor Voltage (VR) for each step in Table-3.
• Calculate Diode Current (ID) using Ohm's Law (ID = VR / R1).

2.2. V-I Characteristic:

• Plot the V-I characteristic graph with Diode Voltage (VD) on the x-axis and Diode Current (ID) on the y-axis.
• Draw a tangent line to the curve around 3mA ID and determine the incremental resistance using the given formula.

3. Zener Diode:
3.1. Basic Zener Diode Circuit:

• Replace the diode with a Zener diode in the circuit (Figure 7).
• Follow the same steps as in the basic diode circuit.
• Record results in Table-4.

3.2. Negative Voltages:

• Apply negative voltages (as given in Table-5) to the Zener diode circuit.
• Record results for Diode Voltage (VZ), Resistor Voltage (VR), and Diode Current (IZ).
• Analyze the Zener voltage characteristics.

3.3. V-I Terminal Characteristic:

• Utilize data from both positive and negative voltage ranges.
• Plot the complete V-I terminal characteristic for the Zener diode.

Answers:

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